I dunno, if I were to pay for a graphic, I think the best way to do it is though a site like sitepoint, where you can judge and give feedback on the images/skin you want, as people compete for the job. Many times graphics just go unused but if they aren't happy with the end product, how can you hold that against them for not wanting to pay for it.
Its like ordering a custom car only to find out it has no engine - you'd send it back until you got the engine